Fresh air is needed if the house construction is tight. There needs to be a minimum number of air changes, ASHRAE suggests 0.3 air changes per hour in a house, more is better, but will cost more too in heating season. Inside air is often more ‘polluted’ than outside air, higher humidity, CO2 from occupants, cooking fumes, off gassing fake wood products, various chemicals used for cleaning, grooming, radon, whatever, if air changes are prevented by tight construction such as 6 mil taped poly vapor barriers, well sealed windows and doors etc.
So fresh air must be brought in. You can open a window, but who is going to do that when it is minus 20? Its a YMMV thing, in milder climates, windows are open, there is plenty of fresh air leaking in to older homes.
I personally would not want to draw my fresh air out of the attic, who knows what is going on up there? There are plumbing vents, chimneys or B vents, leakage of inside air through the ceiling, dust and more dust, I would want my fresh air to come from outside, some place far away from any kind of exhaust, including vehicles.
Bringing fresh air in through the return air is a great solution if you have a forced air furnace, as the air is conditioned, including filtered by the furnace filter.